Ab Initio Investigation of Per- and Poly-fluoroalkyl Substance (PFAS) Adsorption on Zerovalent Iron (Fe⁰)

In this study, dispersion-corrected density functional theory (DFT) calculations were employed to investigate the adsorption of per- and poly-fluoroalkyl substances (PFAS) onto zerovalent iron (Fe⁰). The main objective of this investigation was to shed light on the adsorption properties, including adsorption energies, geometries, and charge transfer mechanisms, for four PFAS molecules, namely, perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), perfluorooctanoic acid (PFOA), and perfluorobutanoic acid (PFBA), on the most thermodynamically accessible Fe⁰ surface facets. Additionally, the DFT investigation examined the role of PFAS chain length, functional group, protonation/deprotonation state, and solvation in water in their adsorption to Fe⁰. Overall, the adsorption of the four PFAS molecules on various Fe⁰ surfaces exhibited thermodynamically favorable energetics. Nevertheless, solvation in water resulted in less exothermic adsorption energies, and the presence of preadsorbed oxygen blocked the Fe⁰ surface, preventing PFAS adsorption. Additionally, the inclusion of a monolayer of Ni on top of the Fe⁰ surface reduced the stability of PFAS adsorption compared to pristine Fe⁰. Results of the computational investigation were compared to experimental results from the literature for qualitative validation.